1. Field of the Invention
The present invention relates to a living body pressing apparatus having a fluid bag, and a living body information measuring apparatus provided with the same. Particularly, the present invention relates to a cuff for a blood pressure monitor, and a blood pressure monitor provided with the same.
2. Description of the Background Art
A blood pressure monitor, a pulse wave detector and others are generally known as living body-information measuring apparatuses for measuring living body information. Normally, the blood pressure monitor and the pulse wave detector each include a living body pressing apparatus. In the state where the living body pressing apparatus is mounted on a measurement site of the living body, a fluid bag contained in the living body pressing apparatus is inflated to press the living body to measure the living body information.
For example, to measure a blood pressure value, a cuff provided with a fluid bag for pressing an artery located within a living body is wound around the body surface, and arterial pressure pulse waves caused in the artery by inflation/deflation of the fluid bag are detected to measure the blood pressure value. Here, the cuff refers to a band-shaped structure having a bladder, which can be wound around a part of a living body, for use in measurement of arterial pressure of an upper limb, a lower limb or the like by introducing fluid such as gas or liquid into the bladder. Thus, the cuff represents the concept including the fluid bag as well as members for winding the fluid bag around the living body. Particularly, the cuff wound around and fitted on a wrist or an upper arm is also called an arm band or a mancheffe.
Recently, blood pressure monitors are often used not only in medical treatment facilities such as hospitals but also in the households as an apparatus for checking the physical conditions day by day. As such, there are strong demands for improvement in handling of the blood pressure monitors, particularly for ease in fitting operation. To this end, downsizing of the cuff has been attempted. To downsize the cuff, it is necessary to narrow the cuff in the width direction (i.e., direction parallel to the axial direction of the measurement site (e.g., wrist, upper arm or the like) to which the cuff is applied).
To narrow the width of the cuff for the blood pressure monitor, it is important to ensure that the artery is sufficiently pressed for avascularization. In the case of using a cuff for a blood pressure monitor having a large width, a long length in the axial direction of the measurement site covered by the cuff can be guaranteed, which enables sufficient pressing and avascularization of the artery. However, if the width of the cuff is narrowed, the length in the axial direction of the measurement site covered by the cuff becomes short, in which case it would be difficult to sufficiently press the artery for avascularization.
A cuff for a blood pressure monitor disclosed in Japanese Patent Laying-Open No. 02-107226 and a cuff for a blood pressure monitor disclosed in Japanese Patent Laying-Open No. 2001-224558, for example, are known as those directed to prevent degradation of avascularization performance in-association with a decreased cuff width. In each of the cuffs for a blood pressure monitor disclosed in these publications, an air bag identified as a fluid bag arranged inside the cuff is provided with a gusset at each side end portion in the width direction. When the air bag is inflated, the gussets expand to make the air bag inflated more uniformly in the width direction. With this configuration, it is possible to sufficiently press the artery for avascularization, not only at the central portion of the cuff, but also at and around the respective side end portions thereof. This ensures accurate measurement of the blood pressure value even if the cuff is narrowed in width.
When the gusset is provided at each side end portion in the width direction of the air bag, however, the side end portion in the width direction of the air bag increases in height in the thickness direction when the air bag is inflated. This may induce lateral displacement of the air bag as will be described below.
FIG. 23 is a schematic diagram showing the state where a typical wrist blood pressure monitor is mounted on a measurement site of the wrist. FIG. 24 is a schematic cross sectional view of the cuff for the blood pressure monitor shown in FIG. 23, taken along the line XXIV-XXIV in FIG. 23. FIG. 25 is a schematic diagram showing the state where there occurs lateral displacement of the cuff for the wrist blood pressure monitor in the measurement state shown in FIG. 23. FIG. 26 is a schematic cross sectional view of the cuff for a blood pressure monitor and the wrist shown in FIG. 25, taken along the line XXVI-XXVI in FIG. 25.
As shown in FIG. 23, the wrist blood pressure monitor 100 includes a main body 110 and a cuff 130. Upon measurement of blood pressure values using wrist blood pressure monitor 100, cuff 130 of blood pressure monitor 100 is wound around the wrist 300 as the measurement site in the circumferential direction. As shown in FIG. 24, cuff 130 primarily includes a cover member 140 in a bag shape, and an air bag 150 and a curled elastic member 160 arranged inside cover member 140. Curled elastic member 160 is elastic and curved to temporarily fit the cuff on the wrist. Cover member 140, air bag 150 and curled elastic member 160 extend with their longitudinal direction corresponding to the winding direction of cuff 130.
Cover member 140 is formed into a bag shape by laying an inner cover 141 made of highly elastic cloth or the like and an outer cover 142 made of less elastic cloth or the like one on the other and connecting their rims. Air bag 150 is formed into a bag shape by laying a resin sheet 151 constituting an inner wall portion located on the wrist side in the fitted state of the cuff and a resin sheet 152 constituting an outer wall portion located on the outer side than the inner wall portion one on the other and melting and bonding their rims, and has an inflated/deflated space 157 therein. Resin sheet 151 constituting the inner wall portion of air bag 150 has its side end portions folded and melted and bonded to resin sheet 152 constituting the outer wall portion, so that gussets are formed at the respective side wall portions of air bag 150. On the outer surface of the outer wall portion of air bag 150, curled elastic member 160 identified as an elastic member which is wound annularly and changeable in size in a radial direction, is attached using an attaching member such as a double-faced tape 171.
In wrist blood pressure monitor 100 of the above configuration, a pump, a valve and the like identified as an inflating/deflating portion arranged inside main body 110 are used to increase or decrease the pressure within inflated/deflated space 157 of air bag 150 arranged inside cuff 130 to inflate or deflate air bag 150. The blood pressure value is calculated based on the pressure information detected during inflation/deflation of air bag 150.
In the state where air bag 150 is inflated, if an external force is applied to outer cover 142 of cover member 140 in the direction parallel to the axial direction of wrist 300, the outer portion of cuff 130 may suffer lateral displacement in the axial direction of wrist 300, whereas the inner portion of cuff 130 will not suffer lateral displacement since it is in contact with wrist 300. This causes a part of cuff 130 to protrude as shown by a reference character 190 in FIG. 25. Even if there is no external force applied, pressure balance of air bag 150 may be lost due to the inclined shape of the surface of wrist 300, which may cause lateral displacement as well.
As shown in FIG. 26, the lateral displacement described above occurs as the pressure balance of air bag 150 is lost at the time of inflation, causing movement of curled elastic member 160, outer cover 142 and resin sheet 152 as a whole in the axial direction of wrist 300. When curled elastic member 160 moves in the axial direction of wrist 300, the air in air bag 150 moves toward the end portion of air bag 150 opposite to the moved direction of curled elastic member 160, which causes deformation of air bag 150, leading to occurrence of the protruding portion 190 described above. When such protruding portion 190 is generated, it is not possible to efficiently and uniformly press air bag 150 against wrist 300, in which case sufficient avascularization performance cannot be obtained, resulting in deterioration of measurement accuracy. Further, the both ends (regions A shown in FIG. 26) of the attached portion of air bag 150 and curled elastic member 160 would suffer a force in the direction causing peeling of air bag 150 from curled elastic member 160, which may degrade reliability of the attached portion.
The lateral displacement described above is more likely to occur as the thickness of inflated/deflated space 157 is greater with respect to the width of air bag 150 at the time of inflation. It poses a serious problem especially in the configuration where gussets are formed at both side end portions of air bag 150 for the purposes of preventing degradation of measurement accuracy attributable to reduction in width of cuff 130. The above problem however is not restricted to the cuff for a blood pressure monitor having such a configuration. A cuff for a blood pressure monitor not provided with the gussets at the side end portions of the air bag would also suffer the problem to some extent, for which a solution is sought.
Besides the blood pressure monitor, a pulse wave detector is also known as the living body information measuring apparatus provided with a fluid bag for use in pressing the living body. The pulse wave detector is an apparatus for measuring pulse waves by pressing a pressure-sensitive device as represented by a semiconductor sensor against a surface of the living body so as to measure pulse waves generated at an artery located relatively close to the skin of the living body. In the pulse wave detector as well, a fluid bag such as an air bag is used as a pressing member for pressing the pressure-sensitive surface of the sensor chip against the living body, which may cause a problem of lateral displacement similar to that of the cuff for a blood pressure monitor described above.